The need to achieve low cost delivery of new bandwidth hungry services such as IPTV (internet protocol television) has required the re-design of the networks for an efficient and flexible packet transport. Transport technologies, historically related to SDH (synchronous digital highway), are evolving towards Ethernet which has a higher networking responsibility.
However the deployment of Ethernet networks demand integration with the optical layer since metro bandwidth requirements has lead to the adoption of DWDM optical transmission systems that rely on a circuit-oriented architecture. Different solutions aiming at reducing capital and operational costs while integrating packet and circuit layers have arisen. For example there are systems based on a single-platform node architecture with multi-layer switching structure. They combine the WDM/OTN optical layer with the new connection oriented Ethernet transport technologies such as PBB-TE (provide backbone bridge traffic engineering) and MPLS-TP (Multi-Protocol Label Switching Transport Profile). Such technologies are able to replicate SDH carrier class performance and provide tunnel switching, allowing removal of coupling between transport and services, and aggregation of flows over WDM wavelengths.
On the other hand there are solutions, such as Matisse “packet WDM”, based on an optical burst switching paradigm that eliminates the need for optical circuits and aims at assuring the “any-to-any” flexibility of Ethernet.
In parallel, high speed Ethernet switches with fully distributed architecture are continuing to evolve to accommodate changes in networked applications and to pave the way for the next generation of Ethernet at 100 Gbps.
Solutions based on MPLS-TP/PBB-TE carrier Ethernet technologies present limited scalability and flexibility, and require a sophisticated control plane to coordinate different switching layers so as to optimize bandwidth utilization. Alternative solutions based on OBS require complex resource management (Medium Access Control (MAC) scheme) to exploit their potentiality in capacity efficiency and at the same time are limited by technology constraints. The current state of the art does not allow, for instance, efficient contention resolution mechanisms due to the lack of practical all-optical wavelength converters.
The best trade-off between connectivity and bandwidth may be achieved through next generation Ethernet switches by solving critical issues such as scalable forwarding performance and robust control functions. Layer 2 Ethernet switching, is expected to dominate next generation networks in the next five years. But Ethernet and packet switching in general has scalability issues owing to the amount of time needed to process every packet. Current distribution mechanisms such as the Ethernet LAG protocol split traffic across multiple links at flow granularity, but may waste resources by up to 60% in dynamic environments. This occurs because flow level granularity do not enable efficient filling of the capacity of the link.